The present invention relates to a brake lining wear detection apparatus for friction brakes, such as drum brakes or disc brakes, for detecting when the brake lining is abraded to or beyond a prescribed quantity, for example, up to a wear limit value.
Friction brakes, such as drum brakes or disc brakes, press a brake lining (brake pads in disc brakes; in the present specification, the brake lining is a friction braking member such as a brake pad) against a brake member such as a rotating brake drum or disc (rotor), and thereby impart a friction braking action to the brake drum. The brake lining is gradually worn away by this friction braking action and when use of the brakes continues beyond this wear limit, effective braking becomes more difficult. For this reason, various brake lining wear detection apparatuses, for detecting when the wear on the brake lining progresses to a certain wear limit and providing a warning to the driver, are proposed.
One such apparatus is an apparatus that directly detects wear on the brake lining. An example of such an apparatus can be illustrated with the apparatus disclosed by this applicant in the specification for Japanese Patent Application Laid-open No. H10-184748.In this apparatus, a detecting jig is disposed from the back surface of the brake lining and faces the brake drum. Metal wiring connected to a warning circuit is embedded in the end of thereof in the form of a loop. The detecting jig is disposed so that the end portion contacts the brake drum when the wear on the brake lining progresses to the wear limit. When the end of the detecting jig is worn or broken by this contact and the metal wiring therein is cut, the warning circuit detects the breakage of the circuit from the change in current or voltage and warns the driver that the brake lining has reached the wear limit.
Other apparatuses indirectly detect the wear on the brake lining. For example, the apparatus disclosed in Japanese Patent Application Laid-open No. H11-351296 detects wear of the brake lining in drum brakes from the amount of piston movement in a wheel cylinder causing the swinging of the brake shoe. In drum brakes comprising an automatic adjusting mechanism, the end position of piston movement gradually moves as the brake lining wears away. By having a rod which moves in conjunction with the piston in the wheel cylinder and monitoring the amount of movement of this rod with a limit switch, [this apparatus] detects when the brake lining has reached the wear limit and then warns the driver.
However, in these types of conventional apparatuses, an electrical circuit that detects wear of the brake lining and transmits a signal is disposed near the wheels, which generate intense vibrations and heat as the vehicle travels. Breakage or disconnection of the electrical wiring or limit switch therefore occurs easily. These must therefore be made vibration resistant and able to tolerate the environment; it therefore becomes difficult to reduce costs.
Also, apparatuses that directly detect wear on the brake lining by the breakage of an electrical circuit have a problem with false detection because of the breakage of the wiring due to the vibrations when the vehicle is moving, as discussed above. Moreover, when the electrical circuit is short circuited, these apparatuses cannot detect when the brake lining has reached the wear limit. When wear on the brake lining has been detected and these detection apparatuses are replaced, the wear detecting jig must also be replaced with a new part at the same time. For this reason, parts costs at replacement result in even higher running costs, and the man hours necessary to connect the electrical wiring also result in increased running costs. These apparatuses also have structural problems such as the risk of wiring being cut due to mistakes during replacement.
It is an object of the present invention to provide a brake lining wear detection apparatus having high reliability, and that can be constituted at low cost with a constitution of simple parts.
The present invention is an apparatus for detecting wear on brake linings in a friction brake (for example, drum brake 3 in the first embodiment or disc brake 5 in the second embodiment) comprising: a lining member (for example, brake shoe 20 in the first embodiment or inner pad 120 and outer pad 120xe2x80x2 in the second embodiment) on which the brake lining (lining 23 in the first embodiment, or pads 123, 123xe2x80x2 in the second embodiment) is provided; a brake member (for example, brake drum 25 in the first embodiment or rotor 125 in the second embodiment) that is pressed and braked by the brake lining when the brake is activated; a pressing member (for example, pressing screw 57, 157 in the first and second embodiments) for pressing the brake lining onto the brake member when the brake is activated; means for generating pressing force (for example, diaphragm, wedge 52, tappet 54 in the first embodiment, or diaphragm, shaft S, operating shaft 152 in the second embodiment) for causing the pressing member to exert the pressing force; a transmission member that screws onto a pressing member between the pressing member and the means for generating pressing force and is disposed rotatably about this screw shaft, and which transmits the pressing force generated by the means for generating pressing force to the pressing member in the direction of the screw shaft (for example, sleeves 56, 156 in the first and second embodiments); and an adjustment mechanism which rotates the transmission member about the screw shaft to cause the pressing member to project according to the wear on the brake lining, and which automatically adjusts the space between the brake lining and the brake member when the brake is not activated so as to become a predetermined, prescribed magnitude. Furthermore, the brake lining wear detection apparatus comprises: rotation detecting means (for example, displacement detection apparatus 70 in the embodiments) for detecting the state of rotation of the abovementioned transmission member or of a rotating member (for example, the wheel of 168 in the second embodiment) which rotates the transmission member; means for storing a number of rotations(for example, controller 30 in the embodiments) that counts and stores the number of rotations of the transmission member or rotating member from the state of rotation detected by the rotation detecting means; and warning means for performing a warning operation when it is determined that the number of rotations stored in the means for storing a number of rotations exceeds a predetermined and stored limit number of rotations.
As the brake lining (pad) is worn away by the action of the brakes (friction braking) in friction brakes comprising the abovementioned adjustment constitution, the pressing member pressing the lining member is caused to project as the abovementioned transmission member is caused to rotate about the screw shaft according to the wear on the brake lining, and the interval between the brake lining and the brake member when the brakes are not in use is automatically regulated so as to become a predetermined, prescribed interval. The number of rotations from the initial state of the transmission member is equivalent to the amount of the projection of the pressing member and is an amount that indicates the amount of wear on the brake lining. The present invention uses the properties of the regulating action of the adjustment mechanism and comprises a brake lining wear detection apparatus [that functions as follows]. The state of rotation of the transmission member or the rotating member that rotates the transmission member during the regulating action is detected with the rotation detecting means. The means for storing a number of rotations calculate and store the number of rotations of the transmission member or rotating member from the state of rotation detected. Then, the warning operation means perform a warning operation when it is determined that the state of rotation stored in the number of rotations storing means has exceeded a predetermined and stored limit number of rotations.
For this reason, the brake lining wear detection apparatus with the abovementioned constitution makes possible high precision detection of the state of wear on the brake lining and also does not require replacement of the wear detecting jig when the brake lining has worn away and the lining members are replaced. Consequently, [this apparatus] reduces parts costs as well as the man hours required for replacement and can therefore keep running costs low; moreover, [this constitution] makes it possible to provide a lining wear detection apparatus with which there is no risk of wiring being cut due to errors made when the lining member is replaced.
Moreover, it is preferable that the brake lining wear detection apparatus be constituted so that the outer surface of the transmission member or rotating member includes a depression or projection (flat surface 56c in the first embodiment, or the gear portion 156a of the wheel 156 in the second embodiment), that is displaced when the transmission member or rotating member is rotated; and the rotation detecting means comprise a shifting member that contacts the outer surface of the rotating member and is displaced along with the depression or projection, and optical detecting means (optical detection system as shown in FIGS. 3 and 4 for the embodiments) for optically detecting the displacement of the shifting member; and so that the state of rotation of the transmission member or rotating member is detected by counting the number of passes of the depression or projection detected in this way.
Because this is a constitution for optically detecting the state of rotation of the transmission member or the rotating member that rotates the transmission member, the wear detection apparatus with the abovementioned constitution can be constituted so as to be highly resistant to electrical noise and the like. Also, the detecting terminal of the optical detecting means and the detection circuit substrate comprising an LED or photodiode are disposed separately. Because these can be connected with a flexible optical fiber with high heat resistance, it is not necessary to include any electronic components such as electrical wiring or a limit switch in the vicinity of the wheels, which generate intense vibrations and heat while the vehicle is moving. Consequently, it becomes possible to provide a lining wear detection apparatus that is highly reliable and has high resistance to vibrations and the environment.
Furthermore, because the state of rotation of the transmission member is detected via the shifting member, the optical detecting means can be optimized to have a small optical detecting portion. Because the transmission member follows the movement in the direction of the screw shaft by the braking action and the rotation about the screw shaft by the adjustment action, it is necessary to dispose the optical detecting portion over a wide area when this [movement] is directly detected. Also, lubricant is necessary in order to ensure the abovementioned movement and powder from abrasion is also generated by the sliding action over long periods of time. However, the constitution of the present invention has the optical detecting portion disposed separately through the use of the shifting member and therefore the optical detecting portion can be made small. Moreover, it becomes possible to have a constitution optimized for optical detection (for example, an optically reflective surface) wherein the effects of abraded dust and lubricating oil are eliminated. Consequently, it becomes possible to provide a lining wear detection apparatus that is highly reliable and can withstand its environment that is also small and low-cost.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.